In known helical scan-type magnetic recording and reproducing apparatus for use in VTRs and DATs, some of guide posts and a drum are inclined with respect to a reference plane and the tape is wound on the drum at an inclination so as to run three-dimensionally, whereby the tape is helically scanned for recording and reproduction. The vertical position of the tape is forcibly limited by flanges on the guide posts and leads of the drum.
Thus, the tape is twisted on the inclined guide posts and drum forcibly by the flanges on the guide posts and the leads of the drum so as to run along a three-dimensional path. This arrangement, however, causes a tension to be developed nonuniformly upon the tape in the breadthwise direction of the tape, thus raising the possibility that the forcible guidance by the posts and drum lead will create a non-linear friction at the edges of the tape, particularly when the tape has been wound on the tape supply reel with a large fluctuation. As a consequence, problems are caused such as generation of jitter and damaging of tape edges. This problem is serious particularly when the tape has a small thickness. In the worst case, the tape cannot run at all. This type of arrangement is also disadvantageous in that it poses a limit on design for thin profile of the whole assembly.
To obviate this problem, a rotary head device for VTRs has been proposed (Japanese Patent Laid-Open Pub. No. 57-40733), in which, as shown in FIGS. 9A and 9B, a slit 104 which extends obliquely to the rotation shaft 103 is formed between an upper drum 101 and a lower drum 102 and, heads 105 are movable along the slit 104. In this rotary head device, a pair of head mounting members 106 with the heads 105 attached to opposite ends thereof are attracted to each other by a magnetic attracting force produced by magnets 111A, 111B, 112A, 112B, so as to clamp, through intermediary of balls 107, a rotary shaft 103 which is on the axis of rotation of the heads 105, so that the head mounting members 106 are reciprocally movable in the axial direction and rotatable together with the rotary shaft 103 in engagement therewith. The balls 107 are received in vertical V-shaped grooves which are formed in the head mounting members 106 and the rotary shaft 103, such that the balls are clamped between the head mounting members 106 and rotary shaft 103 under the magnetic force of the magnets 111A, 111B, 112A and 112B. Rotation of the rotary shaft 103 causes the head mounting members 106 to be moved by the guidance of the upper and lower drums 101, 102, while being rotated within the slit 104, for axial reciprocal movements, which forms helical tracks on the tape which runs on the peripheral surfaces of drums 101, 102 in the direction perpendicular to the axis of these drums.
In such arrangement, a mechanical play (wobbling) is likely to be formed, in view of the balls 107, which allows vertical movement of the heads 105, being held between the rotary shaft 103 and head mounting members 106 which are attracted to each other through the magnetic attracting force of magnets 111A, 111B, 112A and 112B. This play tends to be amplified so as to appear with greater magnitude on the portions of the heads 105 adjacent the outer peripheral surface of the drum. In addition, the mechanical connection between the head mounting members 108 and rotary shaft 103 is quite unstable because they are supported through the balls 107 alone as to the rotational direction. Furthermore, adjustment of clearance is extremely difficult to conduct due to the necessity for the upper and lower guide surfaces 108, 109 for the vertical movement of the head mounting members 106. It is also to be pointed out that the provision of the roller 110 at a contact point, where the head mounting members 106 is contacted with the guide surfaces 108, 109, results in a discordance between the rotational direction of the head mounting members 106 and that of the roller 110, wherein the latter rotational direction is tangential to the former one.